1. Field of the Disclosure
The present disclosure relates to a proximity sensor for detection of an approaching state of an object, and in particular to a proximity sensor that is suitable for application to a portable terminal.
2. Description of Related Art
In recent years, portable terminals called “smartphones” have been widely used. In many smartphones, a touch screen in which a display screen also serves as a touch panel is used. When a user brings his/her ear close to a sound output port of an ear receiver provided at a predetermined location of a housing of such a portable terminal during a conversation or the like, the face or the ear of the user may contact the touch screen. However, such a contact with the touch screen is not intended by the user to be performed on the touch screen.
In the related art, in order not to incur an improper operation of the touch screen in such a case, a proximity sensor is used to sense an approach of an ear or a cheek of the user in order to stop an operation of the touch screen and prevent an improper action of the touch panel.
Usually, a flat window member made of glass, plastic, or the like is provided in a housing member above a light emitting section and a light receiving section of the proximity sensor. If the window member has a large thickness, however, light emitted from the light emitting section may be scattered or reflected inside the window member to directly arrive at the light receiving section. In this case, the proximity sensor may improperly recognize that there is an object in proximity even if there is no such object in proximity to the proximity sensor.
For example, a case where a proximity sensor including a light emitting section 11 and a light receiving section 12 provided on a substrate (circuit substrate) 60 faces a window member 13 provided in a housing 50 as shown in FIG. 2 is considered. In this case, if the window member 13 has an appropriate thickness, an object in proximity 70 is appropriately detected with little of light scattered inside the window member 13 to arrive at the light receiving section 12. Therefore, no improper operation of the proximity sensor is caused.
However, in the case where the window member 13 has a large thickness and thus has a space that is enough for light from the light emitting section 11 to be scattered inside the window member 13 to arrive at the light receiving section 12 as shown in FIG. 3, the proximity sensor may produce a detection output that indicates presence of an object in proximity even when there is no such an object in proximity. Meanwhile, for convenience of mounting a proximity sensor in a portable terminal, the proximity sensor provided on the substrate 60 and the window member 13 may be more or less spaced apart from each other. In this case, it is necessary for the window member 13 to have a large thickness.
An improvement may be achieved by physically separating the light emitting section and the light receiving section from each other in position. In that case, however, it may be difficult to secure a space that allows the light emitting section and the light receiving section to be sufficiently separated from each other in the portable terminal because of a reduced size of the terminal. In the case where a proximity sensor in which the light emitting section and the light receiving section are integrated with each other is used, the distance between the light emitting section and the light receiving section may not be increased any further.
The above issues may be addressed by reducing the power for driving the light emitting section. In this case, however, the distance over which an object in proximity is recognizable may be reduced, and the performance of the proximity sensor may not be satisfactory.
Thus, it is necessary to design the window member such that no improper operation is incurred even in the case where the proximity sensor has a large window thickness.
Japanese Unexamined Patent Application Publication No. 2010-157513 describes a sensing device according to the related art that uses a proximity sensor which senses presence or absence of a foreign object in proximity and an improper action of which is prevented. In the sensing device, a lens section provided above the proximity sensor is structured such that an opaque reflective film is formed inside a transparent lens main body to prevent an improper action of the proximity sensor and enhance the accuracy with which the proximity sensor senses presence or absence of a foreign object in proximity.
However, the device according to the related art includes a large number of components forming the window member, which complicates the manufacture and increases the cost.